Resistance unit



March 19, 1929. G. H. WHITTINGHAM RESISTANCE UNIT Filed June 22, 1926Zlwuentoo Patented Mar. 19, 1929.

UNITED STATES PATENT OFFICE.

GEORGE E. WHITTINGHAM, OF BALTIMORE, MARYLAND, ASSIGNOR TO MONITOR CONTROLLER COMPANY, OF BALTIMORE, MARYLAND, A CORPORATION OF MARYLAND.

RESISTANCE UNIT.

Application filed June 22, 1926. Serial No. 117,763.

This invention relates to resistance units composed of wire coils woundon bodies of refractory material, such as porcelain. Porcelain isdesirable as a support for the windings because of its highheat-resisting and electrical insulating properties, but difficulty isexperienced in satisfactorily securing terminals and other connectors tothe porcelain because of its hard and brittle nature. The purpose of thepresent invention is to provide a resistance unit of this character inwhich connectors can be readily applied to the unit at any desiredpoints, the connectors and insulator being formed so that the formerwill interlock with the latter, and the connectors are held in suchinterlocking engagement by the coil itself.

In carrying out the invention, a metal supporting bar is provided with acovering of refractory material having a plurality of toothed ribs forsupporting the coils of resistance wire, the convolutions of which arewound between and spaced apart by the teeth of the ribs. The refractorymaterial is formed with one or more channels extending longitudinally ofthe bar, and connectors are provided, each having an angular baseadapted to fit between the side walls of the channel, whereby theconnectors will be prevented from turning when their bases are withinthe channels. The bases of the connectors are formed so that they may beinserted into a channel between adjacent convolutions of'the coil, andeach connector is provided with clamping means whereby it may be clampeddirectly to the coil. Thus, the coil serves to hold the connector in thechannel with itsbase on the bottom wall thereof, and prevents movementof the connector longitudinally of the channel, and the interlockingengagement of the base or foot of the connector with the side walls ofthe channel prevents any twisting or turning movement of the connector.

In the accompanying drawing,

Fig. 1 is a side elevation, partly broken away, of a resistance unitmade in accordance with my invention, several forms of connector beingshown on the unit;

Fig. 2 is a section on the line 22 of Fig. 1;

Fig. 3 is a top plan view of the right hand end of the unit shown inFig. 1;

Fig. 4 is a detail perspective view of one form of connector; and,

The covering 7) is preferably of porcelain,

because of its high insulating and heat-resisting properties, and itiscomposed of a series 0t relatively short sections 3, 4, and 5, fittingover the upper half of the bar, and a complementary series of similarsections 3", 4 and 5 fitting over the lower half of the bar. Thesesections are slotted longitudinally to fit over the bar, as clearlyshown at 6 in Fig. 2. The covering has a plurality of toothed ribs 7, 8,9, 10, 11 and 12, and the resistance coil 0 is Wound over these ribs andits convolutions are spaced apart by the teeth of the ribs. Between theribs '1 and 8 is a channel 13, and between the ribs 10 and 11 is asimilar channel 13. These channels have relatively fiat bottom walls andparallel sides and extend throughout the len th of the covering and areopen at their en s.

In the channel 13 are shown terminals (l, of the type shown in detail inFig. 4, each terminal formed from a sheet metal strip and composed of abody portion 14, constituting a binding post, and a part 14' bent overat right angles to the body portion to form a base or foot. The end ofthe base is turned downwardly, forming a flange 14 As shown, the basesof the terminals d are arranged within the channel 13, in Fig. 1,beneath the wire coil, and the bases of the terminals rest upon nuts 15,which fit within the channel. A clamping screw 16 extends through thebase 14 and into the nut 15, and a washer 17, under the head of theclamping screw, clamps two convolutions of the coil between said washerand the foot 01" the binding post. Thus, the binding post is secured tothe insulator by the coil and is prevented from turning by the sidewalls of the channel. The terminals (5 may be applied While the coil isbeing wound upon the insulator, and the ends of the coil are secured tothe binding posts by screws 18.

The connector d is the same as the terminal connectors cl except thatthe nut is not shown associated with the base of the connector d. Theform of the connector is such that the base or foot may be inserted intoa channel through the space between two adjacent convolutions of thecoil, and when the base of the connector is turned parallel with thechannel, it may be secured to the coil by the clamping screw and the nutmay or may not be used, as desired. If it is desired to place a nutunder'the base of the connector 03, the nut may be inserted into thechannel through one of its open ends and pushed along the channel untilit is stopped by the flange on the connector base, and the clampingscrew may then be inserted through the base and into the nut.

It will be evident that a connector such as d or d may be readilyattached to the unit at any desired point. With this form of connector,the clamping screw passes between two adjacent convolutions of the coiland these two convolutions are directly connected electrically to theconnector. This is an advantage where the current taken off through theconnector is heavy, but it may be a disadvantage in some instances,especially where numerous connectors are applied to a coil because eachconnector short circuits one convolution of the coil. A form ofconnector is shown at e and e which engages only one convolution of thecoil. This connector is made from a sheet metal strip and comprises thebody portion 19, having one end turned over to form a foot or base 19(Fig. 3) and a clamping member 20, made from a strip of metal of thesame width as that of the post 19 and having a part 20 turned outwardlyat right angles to the body portion to form a foot, and having a flange20 at its upper end, adapted to bear against the post 19 and space thepart 20 from said post. A clamping screw 21is provided for clamping theparts together. This connector may be secured to the coil at any pointby inserting the base of each part separately into a channel at oppositesides of a convolution of the coil, and by then inserting the clampingscrew through the parts and drawing them tightly together the connectorwill be secured to the convolution of the coil and will be held in placewithin the channel by said convolution.

In the several forms of connector shown,

the insulator, connectors may be applied at points close together in thelength of the coil and at diiferent angles with respect to the body ofthe resistance unit.

For convenience in connecting the terminal of one unit to the oppositeterminal of another unit, and for connecting the units in various ways,each section of insulating material is formed with semi-circular grooves22 (Fig. 2) on its inner face, and when the sections are broughttogether on the supporting bar these grooves form circular openingsthrough the insulator and the connecting wires may be extended throughthese openings.

What I claim is 1. A resistance unit comprising a metal supporting bar,an insulating covering of refractory material thereon, said coveringcomprising two series of opposed complementary sections, grooved to fitthe bar, each sect-ion having toothed ribs and a channel between saidribs extending longitudinally of the bar, said channel havingsubstantially parallel side walls and a relatively fiat bottom wall, awire coil-wound over said ribs, and a connector comprising a post havinga fiat metal foot insertable into said channel between convolutions ofthe coil, the foot of said post fitting within the channel and heldagainst turning movement by the side walls thereof, and means forclamping said connector to the coil.

2. A resistance unit comprising a metal supporting bar, an insulatingcovering of refractory material thereon, said covering comprising twoseries of opposed complementary sections, grooved to fit the bar, eachsection having toothed ribs and a channel between said ribs extendinglongitudinally of the bar, said channel having substantially parallelside walls and a relatively flat bottom wall, a wire coil wound oversaid ribs, and a connector comprising, two metal strips arranged atopposite sides of a convolution of the coil and each having a footinsertable through the space between adjacent coils and fitting betweenthe walls of a channel, and means for clamping said strips against saidconvolution of the coil.

3. A resistance unit comprising a metal supporting bar, an insulatingcovering of refraotory material thereon, said covering comprising aplurality of complementary sections arranged on opposite sides of thebar, said sections having opposed slots through which the bar extendsand having opposed channels spaced from said slots and forming alongitudinal passageway through the covering at one side of the bar anda resistance coil on said covering.

In testimony whereof I hereunto afiix my signature.

GEORGE H. WHITTINGHAM.

